1. Field of the Invention
This invention relates to disk drives. More particularly, it relates to a head disk assembly for a hard disk drive having a washer between a disk clamp and disk and method of making such a head disk assembly.
2. Description of the Prior Art and Related Information
Typically, the main assemblies of a hard disk drive are a head disk assembly and a printed circuit board assembly.
The head disk assembly includes an enclosure including a base and a cover, at least one disk having at least one recording surface, a spindle motor for causing each disk to rotate, and an actuator arrangement; a disk clamp is typically used to clamp each disk to the spindle motor. The printed circuit board assembly includes circuitry for processing signals and controlling operations. Actuator arrangements can be characterized as either linear or rotary; substantially every contemporary cost-competitive small form factor drive employs a rotary actuator arrangement.
In the course of assembling a head disk assembly, one of the stages typically includes installing a disk stack to a spindle motor mounted in a base. A disk stack typically includes a plurality of disks and a spacer positioned between any two given disks. The plurality of disks includes at least a top disk and a bottom disk. After the disk stack is installed, a disk clamp is typically used for clamping the disk stack to the spindle motor using a plurality of screws; the disk clamp includes a bottom surface, a portion of which abuts a top recording surface of the top disk. When the disk clamp is initially installed, the screws are partially tightened to apply an axial load on the disk stack to allow the disk stack to rotate in unison during a subsequent balancing step. After the disk stack is balanced, the screws are finally tightened to securely clamp the disk clamp to the spindle motor.
When the screws are finally tightened, the portion of the disk clamp which abuts the top recording surface of the top disk transfers radial loads to the disk stack such that the disk stack shifts radially relative to a longitudinal axis of a shaft of the spindle motor. This shifting of the disk stack results in the disk stack becoming imbalanced if a sufficient amount of shift has occurred. When the imbalance occurs, the screws and the disk clamp must be discarded and new parts must be used to again clamp the disk stack to the spindle motor. Also, the disk stack must be balanced again which increases the assembly time of a head disk assembly.